June 11, 2007 -- Infants who receive antibiotics in their first year of life
are more likely to develop asthma by age 7, and multiple courses of the drugs
boost the risk more, a Canadian study suggests.

"In children receiving five or more courses of antibiotics in the first
year, the risk of asthma was 1.5 times more likely than in children getting no
antibiotics [during their first year]," study researcher Anita Kozyrskyj,
PhD, tells WebMD. Kozyrskyj is associate professor of pharmacy and medicine at
the University of Manitoba in Winnipeg, Canada.

The study was published in the June issue of the journal Chest.

"The link between antibiotics and asthma was seen in children born to
mothers without asthma, who are considered at low risk," Kozyrskyj says.
And the link held even after other risk factors were taken into account.
However, the study shows having a dog in the household while the child is a
baby confers a protective effect.

Asthma affects almost 5 million children under age 18 in the U.S., according
to the American Academy of Allergy Asthma & Immunology, including 1.3
million children under age 5.

Antibiotics and Asthma Risk

The new research adds to an ongoing debate in recent years about the effect
early antibiotics may have on a child's risk of developing asthma. Kozyrskyj
says research results are mixed; some studies, like hers, show an association
(but not necessarily cause and effect), while other studies do not.

A report released in 2006 that analyzed five different studies found that
infants who got even one course of antibiotics during their first year may have
double the risk of getting asthma later in childhood than babies who received
no antibiotics for their first 12 months.

Kozyrskyj and her colleagues used a prescription database from the
University of Manitoba and McGill University in Montreal to monitor the
antibiotic use of 13,116 children from birth to age 7 years. They noted in
particular the antibiotic use in the first year and whether the child had
developed asthma by age 7.

When antibiotics were given, the reason was noted -- including lower
respiratory tract infections (such as bronchitis), upper respiratory tract
infections (such as ear infection), or nonrespiratory tract infection (such as
urinary or skin infections). Researchers also noted each child's risk factors
for getting asthma, such as having a mother with asthma.

Besides looking at the records, "we also sent out a one-page survey to
ask additional questions," Kozyrskyj says. Researchers asked parents to
note whether children were exposed to tobacco smoke as infants and whether the
household included dogs or cats.

More Findings

Within the group, 6% of the children had asthma by age 7. Antibiotic use was
widespread, with 65% of the children having been prescribed at least one course
of the medication during the first year of life.

The researchers found that for children who got the medications for
nonrespiratory infections, the risk of getting asthma by age 7 was nearly twice
as likely as children who got no antibiotics from birth to age 1 year.

The finding strengthens the idea that early antibiotic use and asthma are
linked, Kozyrskyj says. "In that case you can't say maybe [the asthma] was
due to the respiratory tract infection."

If the household of children taking multiple medication courses did not have
a dog, the children's risk of getting asthma doubled, she found.
"Dogs bring in different germs," she says. And that could strengthen a
child's immunity.

In the study, cats didn't offer the same effect, she says, and may actually
boost risk, although the evidence for that in the study was weak.

Explaining the Link

Exactly why the early antibiotic use may boost asthma risk later isn't
certain, Kozyrskyj says. She speculates that because antibiotics can kill off
the microflora (natural bacteria) in your intestinal tract, "it may change
your immune system, making you more vulnerable to developing asthma."

Still, she emphasizes, asthma is a complex disease. "It's also genetic.
We've identified one factor." But many factors underlie the condition, she
says.

Second Opinion

One strength of the study, according to an allergist not involved in it, is
that the researchers found the link held up between antibiotics and asthma not
just for the children who were treated for respiratory infections.

"The researchers make the argument that these kids [treated for
nonrespiratory infections] were not destined for asthma" yet developed it
after the antibiotic treatment, says William Anderson, MD, a board-certified
allergist in Bellingham, Wash.

Advice for Parents

When your child has an infection and your child's doctor suggests an
antibiotic, what's best? "A parent might question the need for an
antibiotic," Anderson says, and ask about other options. But, he
emphasizes, "there are cases when a kid really needs an
antibiotic."

Kozyrskyj agrees that antibiotics are sometimes crucial, although she notes
the trend among physicians and pediatric groups is to encourage more judicious
use of antibiotics due to antibiotic resistance and other potential
problems.

But, Kozyrskyj says, if your child does need an antibiotic, you can ask your
child's doctor if it is possible to use a narrow-spectrum antibiotic rather
than a broad-spectrum (effective against a wider range of bacteria)
cephalosporin (a class of antibiotics). In her study, she also found that
broad-spectrum cephalosporin antibiotics (such as Ceftin and Cefzil) boosted
the risk of getting asthma more than other antibiotics.